COLOURS PRODUCED BY RA YS 3
results, for with this gas the light due to the positive rays is a
most gorgeous red, while that due to the cathode rays is pale
blue; with helium the positive rays give a reddish light while
that due to the cathode rays is green. The spectroscopic ex-
amination of the light due to the positive and cathode rays
reveals interesting differences which we shall have to consider
later; we may anticipate, however, so far as to say that the
character of the light produced by the positive rays is similar
to that of the velvety glow which, in an ordinary discharge
tube with an unperforated cathode, spreads over the surface of
the cathode.

As in Goldstein's experiments these rays were observed
streaming through holes or channels In the cathode; he called
them u Kanalstrahlen ". Now that they have been proved to be
streams of particles, the majority of which are positively
electrified, it seems advisable to call them positive rays, as in-
dicating their nature; the name Kanaistrahlen only suggests
the methods of demonstrating them.

Many important properties of the positive rays can be
easily demonstrated by the use of a tube like that shown in
Fig. 2. For example when the rays strike against the glass
sides of the tube they make the glass phosphoresce. The
phosphorescence produced by the positive rays is of a different
colour from that produced by the cathode rays and is in
general not nearly so bright. With German glass the positive
and cathode rays both produce a greenish phosphorescence,
though the greens are of different shades. With some sub-
stances the contrast is much more striking, for example with
fused lithium chloride the phosphorescence produced by the
positive rays is an Intense red showing when examined by the
spectroscope the red lithium line; the phosphorescence due to
the cathode rays is a light blue giving a continuous spectrum.
The phosphorescence due to the positive rays is a most